The 14x12 feels like it is glued to the stand. The national has some weight to it too, although a bit less. Feels quite solid and on last inspection they were starting to cap stores and had drawn all frames. The nuc is a maisemore poly and feels a lot lighter in comparison, but of course it's half the size and not wooden. I'd guess it is around 10kg and certainly not getting lighter.
Thanks for all your replies.
I'm reasonably happy that it isn't robbing. To be honest, the nuc has struggled all summer after arriving in a poor state (swarm had made an open nest in a bush, which fell out). So if they're not strong enough by now to defend a small entrance, they're probably in trouble in general.
I'll keep an eye on them all but will...